1. Field of the Invention
The present invention relates to a contact that is pressed on an electrode of electronic equipment consisting of IC (integrated circuit) or LSI (large scale integrated circuit) in order to take out an electrical signal from the electrode. The invention also relates to inspection equipment and electronic equipment which are equipped with the contact.
2. Description of the Background Art
An inspection socket is used for taking out electrical signals from electrodes of electronic equipment consisting of an IC or LSI through contacts by pressing the contacts onto the electrodes in order to inspect the electrical continuity of the electronic equipment. A connector is used for the purpose of maintaining electrical continuity with electronic equipment such that contacts are pressed on the land electrodes of the electronic equipment so as to maintain electrical continuity with the electronic equipment through the contacts. The inspection socket and connector are provided with a number of contacts corresponding to the number of the electrodes of the electronic equipment to be connected, and higher density mounting corresponding to high density electronic equipment is demanded of the contacts to be provided in the inspection socket and the connector.
For example, a contact for BGA (ball grid array) is one of such known contacts. The contact has a planar spiral shape before contacting a ball electrode, and the spiral shape of the contact changes corresponding to the shape of the ball electrode as a result of contacting with the ball electrode (see Japanese Patent Application Publication No. 2002-175859). It is described therein that this contact can meet high density mounting of electrodes, securing electrical continuity without deforming a ball electrode and being highly reliable.
In the case of using a spiral contact, the sag amount increases as distanced from the tip part of the ball electrode while the sag amount of the spiral is small at the tip part. Accordingly, the bending stress most increases near the root of the spiral contact, where it least tends to bend, and therefore the reliability decreases according to the increase in the mounting density of ball electrodes. A known method to solve such a problem is that the shape of an electrode on the side of electronic equipment is designed to be a circular cone, triangular pyramid, quadrangular pyramid, or the like (see Japanese Patent Application Publication No. 2003-78078).
A known inspection contact is, for example, a contact having a spring of spiral shape in which the coil diameter decreases gradually from an outer periphery to an inner circumference. The contact attains electrical continuity by being pressed on the electrode of electronic equipment (see Japanese Patent Application Publication No. 2001-235486). It is stated that since this contact has a spring of spiral shape, the length thereof becomes short as compared with a spring having a uniform coil diameter and that accordingly, the impedance in the spring part decreases, resulting in the decrease of the attenuation of the electrical signal even in the case of detecting a high frequency electrical signal.
There are various methods for manufacturing these spiral contacts: a method in which a plating method is combined with a lithography method that uses ultraviolet radiation (UV) having a wavelength of about 200 nm; a method using laser, etching or punching; or a mechanical method in which a plate is curled up, etc. However, with the lithography method using UV, or the methods using laser, etching or punching, only spiral contacts having a thickness of about 20 μm or less can be obtained, and consequently the aspect ratio is small. Accordingly, the spring becomes thin if it is attempted to increase a stroke (sag amount of a spiral) in order to obtain a contact having high conduction reliability. Therefore, such contacts cannot conduct an electric current of 0.5 A or more.
Also, because of the small aspect ratio, the number of spirals becomes less, and the contact load decreases when the stroke is attempted to be enlarged, whereas the stroke decreases when the contact load is attempted to be increased. Therefore, only spiral contacts of low coupling reliability are obtained. Moreover, because of a large number of parts such as a spiral contact, interposer board with VIA, etc., the cost of parts increases, and the assembling cost increases because alignment is necessary in the assembling, which results in high cost of the contact. On the other hand, if it is attempted to manufacture a spiral contact by machine processing such as curling up of a plate, there is a limit to miniaturization of the contact, and it is difficult to manufacture a large quantity of precision contacts exactly and with satisfactory reproducibility.